text: Sedimented BOD does not directly consume oxygen and this should therefore be taken into account. This is done by introducing a rate of BOD removal combined with a rate of oxygen consumption by BOD. Giving a total rate for oxygen removal by BOD 
  where
  *  is the rate of oxygen consumption by BOD, usually in .
  *  is the rate of settling of BOD, usually in .
  The change in BOD over time is described as
  where  is the BOD from organic matter in the water .
   is typically in the range of 0.5-5 .